I work in the field of information systems and cultural heritage. A significant part of my work is related to the description of things that are of interest to cultural heritage specialists such as archaeologists or anthropologists. These things include objects such as paintings, tools or utensils; structures such as buildings or caves; places such as mountains or towns; etc. Most of the time, the things we need to describe are real, i.e. we can perceive them through our senses and thus give a conventional account of them. However, sometimes we need to deal with things (of the above mentioned kinds) that are imaginary, such as Atlantis (an imaginary place) or Excalibur (the sword which Merlin supposedly got from the Lady of the Lake).
The consensus between researchers seem to be that a sword is a sword is a sword, and thus imaginary swords are described in terms of their purported physical properties, use, chronology and other attributes very much like any real sword. Of course, one would note down that this particular sword happens to be imaginary, and one should not expect to find it in a museum.
However, places are trickier to deal with. The essence of a place seems to be its spatial location, and imaginary places often lack that, i.e. they don't have a well-defined or known location. For this reason, researchers rarely describe imaginary places in the same terms as they would describe real places. Rather, they use accessory attributes (such as what happened there or who lived there) instead of their physical location in the world.
After thinking for a while about this, I am wondering about the nature of imaginary things. For objects (such as the sword in my example), imaginary and real don't seem to differ that much. For places, however, the difference is crucial.
So my question is, are there any works on the ontology (and/or epistemology) of the imaginary that I can look at? Are there any mainstream or accepted takes on this problem? Thank you.